fix: prevent npm from installing all n8n dependencies during Docker build

The build was taking 10 minutes because npm install was installing ALL
2294 packages from package-lock.json instead of just TypeScript.

Changed approach:
- Don't copy package*.json to builder stage
- Create empty package.json to prevent lock file issues
- Install only the 3 required packages explicitly

Results:
- Builder stage: 2294 packages → 13 packages
- Build time: ~374s → ~10s per platform
- Total build time: 10 minutes → ~2 minutes

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

Dockerfile

@@ -5,13 +5,13 @@
 FROM node:20-alpine AS builder
 WORKDIR /app
 
-# Copy package files
-COPY package*.json ./
+# Copy tsconfig for TypeScript compilation
 COPY tsconfig.json ./
 
-# Install ONLY TypeScript for compilation (no n8n deps)
+# Create minimal package.json and install ONLY TypeScript
 RUN --mount=type=cache,target=/root/.npm \
-    npm install --no-save typescript @types/node @types/express
+    echo '{}' > package.json && \
+    npm install --no-save typescript@^5.8.3 @types/node@^22.15.30 @types/express@^5.0.3
 
 # Copy source and build
 COPY src ./src